Javier Valdez founded a magazine in 2003 that focused on drug cartels.
Photograph: Hector Guerrero/AFP/Getty Images

A prominent, award-winning Mexican journalist famed for fearlessly covering drug cartels has been murdered, adding to the already long list of reporters killed this year in what is the most dangerous country in the world for members of the media..

Javier Valdez, who founded and edited the weekly newspaper Ríodoce in Culiacán, capital of the western state of Sinaloa and long a den of drug cartel activities, was driving when he was pulled from his car and shot dead around noon on Monday by a lone gunman, according to early press reports.

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“The murder of Javier Valdez tells us that in Mexico the life of a journalist is completely worthless to those in power,” said Esteban Illades, editor of the Mexican magazine Nexos.

“Journalists are completely expendable: they are either a nuisance you can easily get rid of or someone to pay off, but never someone worth protecting,” added Illades, who knew Valdez and described him as “one of the good ones”.

Mexico has become one the most lethal counties in the world to work in the media as most murders of reporters go unsolved and unpunished. State and local governments often make advertising conditional on positive press coverage, and often demonstrate a crushing lack of interest in investigating crimes committed against the media workers, according to critics.

The murder of Valdez, who also worked for the Agence France-Presse news wire, followed news over the weekend that seven journalists in Guerrero state to the south of Mexico City were surrounded by an estimated 100 gunmen, beaten and robbed of their equipment. The state governor blamed a drug cartel for the attack.

Earlier in the year, the reporter Miroslava Breach, who reported on organised crime, was assassinated as she drove her son to school in the northern city of Chihuahua. The owner of Norte, a newspaper she contributed to, subsequently quit publishing, citing journalist safety.

Journalists on Monday voiced their indignation with yet another killing of a colleague.

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The Committee to Protect Journalists counts 41 reporters in Mexico murdered for their work since 1992 with another the motives for another 50 slain reporters still uncertain. Criminal gangs were blamed in 63% of the murders of journalists.

Founded in 2003, Ríodoce focused on drug cartel activities, a treacherous topic for journalists in Mexico, where cartels kill reporters digging too deeply or retaliate with violence for stories not meeting with their approval. Assailants lobbed a grenade into the Ríodoce office in 2009 after the publication of an investigation titled Hitman: Confession of an Assassin in Ciudad Juárez.

“In Culiacán … to do journalism is to tread an invisible line drawn by the bad guys, who are in both drug trafficking and the government,” Valdez said after being given one of the 2011 International Press Freedom Awards.

Sinaloa state has turned violent in recent months as warring factions fight for control of the Sinaloa Cartel once headed by imprisoned drug boss Joaquín “El Chapo” Guzmán – who was extradited to the United States in January and currently awaits trial in New York.